Jacketed firetube system for a process vessel

ABSTRACT

A jacketed firetube system for use in a process vessel such as a heater or heater/treater has a jacket which extends along the firetube, at a flame inlet end. The jacket can be external to the firetube or internal to the firetube. A heat transfer fluid is circulated along the firetube between the jacket and the firetube for recovering heat from the firetube and reducing the firetube&#39;s temperature. The recovered heat is reintroduced into the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application 61/434,258, filed Jan. 19, 2011, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the invention relate to firetubes for use in process vessels, such as heaters or heater/treaters used in the oil and gas industry, and more particularly, to apparatus and systems for maximizing heat recovery from the firetube and for minimizing fouling and localized overheating.

BACKGROUND OF THE INVENTION

It is known to heat process fluids in a variety of vessels, such as ASME code process vessels, atmospheric bath heaters and tanks. Generally a “U” tube heat exchanger is fit within the process vessel. Heat is transferred from the heat exchanger to the process fluids therein for heating the process fluids as part of the handling and refining operation.

In the oilfield, U-tube heat exchangers or U-shaped “firetubes” are common for use in separation vessels such as heater-treaters and free-water knockout vessels and in line heaters and tanks. Traditionally, the firetube, generally made of one or more sections of round, steel pipe, is heated by a burner which is connected to an inlet end of the firetube and discharges flame and exhaust gases to the firetube for passage therethrough. A vent or exhaust stack at an outlet end of the firetube discharges heat-depleted exhaust gases therefrom. Any heat remaining in the exhaust gases is typically lost to the exhaust stack.

In a direct-fired vessel, the firetube is immersed in process fluid contained in the vessel. An external surface of the firetube is in direct contact with the process fluid for effecting the heat transfer thereto. Heat is transferred from the hot gases passing through in the firetube by transfer through the firetube's wall and directly to the process fluid.

Conventional firetubes are built in a “U”-shape, having the burner end and the exhaust stack end fit at a common wall. The “U”-shape extends into the vessel from the common wall. The common walls of one or more firetubes are installed inside the vessel through one or more obround or oval shaped manways in a front wall of the vessel.

It is known in the oil and gas industry that hydrocarbon-based process fluids, such as hydrocarbon emulsions, contain not only hydrocarbon and water, but may also contain contaminants such as polymers, solids, sand and the like. Polymer additives are often used in operations on subterranean hydrocarbon-bearing formations including water flood recovery. Accordingly, fluids returned from the formation contain not only oil and water, but also contain significant amounts of polymer. In fluid recovery vessels, clean, dry product oil is recovered from contaminant-rich, hydrocarbon returned fluids including emulsions. The returned fluids are directed to a conventional heater/treater vessel for separation therein. In the case of a direct-fired heater vessel, contaminants and particularly the polymers, are susceptible to attaching to the very hot external surfaces of the firetube, resulting in a coating or fouling of the firetube's surfaces and reducing the ability to effectively exchange heat to the process fluids.

Further, in automated operations, as the monitored temperature of the process fluid does not increase to desired operational temperatures or even lowers, the control system increases the burner input in response. Increased burner input results in a larger flame which can cause flame impingement at inside walls of the firetube, impingement creating localized hot spots. Hot spots can ultimately result in burn-through of the firetube walls. Applicant is aware that in some cases, firetubes in polymer-contaminated process vessels can be changed out as frequently as every two weeks.

Clearly there is a need for means to extend the service life of the firetube, particularly when the process fluid to be heated is a contaminant or polymer-rich fluid emulsion.

SUMMARY OF THE INVENTION

Embodiments of a jacketed firetube system efficiently utilize and conserve heat within a direct-fired heater and protect the firetube from developing hotspots, by circulating a heat transfer fluid, externally or internally, along at least the portion of the firetube which is at greatest temperature.

In one broad aspect, a method for recovering heat from a firetube immersed in a process fluid in a process vessel, for heating the process fluid, comprises circulating a cool heat transfer fluid in a circulation circuit in thermal communication with and extending along at least a portion of the firetube and therewith. Heat is recovered from the firetube for heating the heat transfer fluid therein and thereafter heat is transferred from the heated, heat transfer fluid to the process fluid.

In another broad aspect, a jacketed firetube system is used to transfer heat from a firetube to a process fluid in a process vessel where the firetube is adapted for connection to a burner at a first burner end and a vent stack at a second outlet end and having a passageway therebetween for directing hot gases from the burner to the vent stack. The firetube is immersed in the process fluid. The jacketed firetube system comprises a circulation circuit extending along at least a portion of the firetube for circulating a heat transfer fluid therein. The circulation circuit comprises a tubular jacket, extending along the firetube from the first burner end along at least a portion thereof, the jacket in thermal communication therewith and defining a circulation space therebetween. An inlet to the jacket delivers cool, heat transfer fluid to the circulation space. An outlet from the jacket discharges heated, heat transfer fluid therefrom. The heat transfer fluid is circulated through the circulation space for recovering at least a portion of the heat from the firetube.

Process vessels can be manufactured using embodiments of the jacketed firetube system and existing process vessels can be retrofit using embodiments which can be inserting internally into the conventional firetube or the conventional firetube can be removed and an external jacketed firetube embodiment inserted into the vessel.

Using embodiment of the jacketed firetube system, Applicant believes the efficiency of the firetube increases from a conventional efficiency in the range of about 60% to about 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a prior firetube installed in a vessel and immersed in fluid therein, a portion of the vessel having been removed for clarity;

FIG. 2 is a side view of a jacketed firetube system according to an embodiment, having a jacket external to the firetube and enclosing the entirety of the firetube therein, a portion of the vessel having been removed for clarity;

FIG. 3 is a side view according to FIG. 2, a divider wall being positioned in the jacket between a first and second leg of the U-tube firetube for directing fluid circulated therein;

FIG. 4 is a side view of a jacketed firetube system according to another embodiment, the external jacket extending along only a portion of the firetube and enclosing a portion of the first and second legs therein, a portion of the vessel having been removed for clarity;

FIG. 5A is a side view of a jacketed firetube system according to another embodiment, the external jacket extending along the first leg of the firetube, a portion of the vessel having been removed for clarity;

FIG. 5B is a cross-sectional view along section lines B-B according to FIG. 5A;

FIG. 6 is a side view of a jacketed firetube system according to another embodiment, an internal jacket insert extending within and along the first leg of the firetube, a portion of the vessel having been removed for clarity;

FIG. 7A is a cross-sectional view of the internal jacket insert according to FIG. 6;

FIG. 7B is a perspective view of the internal jacket according to FIG. 6;

FIG. 8 is a side view of a jacketed firetube system according to an embodiment installed in a heater or heater/treater vessel where the heat transfer fluid is a vessel product fluid, illustrating fluid connections between the vessel and the jacketed firetube;

FIG. 9 is a side view of a jacketed firetube system according to an embodiment installed in a heater or heater/treater vessel where the heat transfer fluid is a fluid incompatible with the process fluid, illustrating fluid connections between the vessel, a heat exchanger and the jacketed firetube;

FIG. 10 is a partial side view of a jacketed firetube having thermal conducting passageways in the firetube; and

FIG. 11 is a partial side view of a jacketed firetube having thermal conducting passageways in the jacket.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Having reference to FIG. 1, a prior art heater system for a process vessel V for heating a process fluid F is shown. An example of a process fluid F treated in such a vessel V is a contaminant-rich hydrocarbon process fluid emulsion. The heater system comprise a firetube 12 having a first burner end 14 adapted for connection to a burner B, a second outlet end 16 adapted for connection to an exhaust stack X and a passageway A therebetween for conducting hot gases G from the inlet 14 to the outlet 16. The prior art firetube 12 is immersed directly in the process fluid F to be heated in the vessel V. Heat which is not transferred from exhaust gases G flowing through the firetube 12 to the process fluid F is lost to the exhaust stack X. Further, at least a portion of the firetube 12, particularly at the first burner end 14 adjacent the burner B, is exposed to the flame and is at an elevated temperature. This high temperature portion of the firetube is at risk, to itself and to the process fluid. The high temperatures are detrimental to process fluid F and to the firetube 12 as a result, particularly when the process fluid F contains polymers, causing fouling of the firetube 12. Fouling of the firetube 12 causes a reduction in heat transfer efficiency and the encouragement of the conditions for formation of hotspots.

Applicant understands that, in a conventional U-tube firetube 12, this high temperature portion corresponds, at least in part, to the flame portion from the burner B, typically extending from the first burner end 14 of the firetube 12 about ⅓ of the outgoing length of the firetube 12. Longer firetubes 12 receive greater input with greater flame lengths, still being in the order of ⅓ of the outgoing length. Temperatures, in the first ⅓ of the firetube 12, can typically reach about 1300° F., depending upon system parameters.

As shown in FIGS. 2-9, embodiments of a jacketed firetube system 10 comprise a U-shaped firetube 12, having the first burner end 14 adapted for connection to the burner B and the second outlet end 14 adapted for connection to the exhaust stack X. The burner B discharges flame and exhaust gas G along a firetube bore 11.

The system further comprises a circulation circuit 17 for recovering heat from the firetube 12, extending from about the first burner end 12. A heat transfer fluid P, such as an unheated or cool heat transfer fluid P_(c), is circulated along at least a portion of the firetube 12, particularly along a high temperature portion TH, extracting heat therefrom and producing a heated heat transfer fluid P_(h). As a result, the temperature of the firetube 12 along the high temperature portion TH is reduced, recovering maximal heat therefrom, and reducing the temperature below that temperature which is detrimental to the heat transfer fluid P and ultimately detrimental to the firetube 12. While shown in the context of a U-shaped firetube 12, conveniently supported from a common front wall 20, the heat recovery and embodiments herein can also be applied to other straight and arcuate firetubes having different interfaces with the vessel V.

The heat transfer fluid P may be a product fluid produced by a treatment of the process fluid, or may be another fluid, such as gycol.

The circulation circuit 17 comprises structure extending along at least the high temperature portion TH and forming a fluid passageway for placing the heat transfer fluid P in thermal contact with the firetube 12. The circulation structure comprises a tubular jacket 18 which extends from the firetube's first burner end 14, adjacent the burner B, and along the at least a portion of the firetube 12 where the temperature of the firetube 12 is highest. The jacket forms a circulation space C between itself and the firetube 12. The jacket 18 is closed, such as by an annular front wall 21 and an end wall 22. The circulation circuit 17 further comprises a jacket inlet 30 which receives and delivers the received, cool heat transfer fluid P_(c) to the circulation space C and a jacket outlet 32 which discharges heated heat transfer fluid P_(h) therefrom.

In the embodiment of FIG. 2, the tubular jacket 18 is external to the firetube 12, enclosing the entirety of the U-shaped firetube 12 therein. As shown, a conventional U-shaped firetube 12 has a first outgoing leg 13 extending from the first burner end 14 to a U-shaped bend 36 and a second return leg 15 extending from the U-shaped bend 36 to terminate at the second outlet end 14. The first burner and second outlet ends 14, 16 extend through the front wall 21 of the jacket 18 for connection to the burner B and exhaust stack X. The jacket's front wall 21 can also act or form the common front wall 21 for connection of the firetube 12 to the vessel V. Hot exhaust gases G flow through the firetube 12 from the first burner end 14 to the second outlet end 14. The jacket inlet 30 and jacket outlet 32 are connected to the jacket 18 at the jacket's front wall 21.

In an embodiment, best seen in FIG. 3, a divider wall 34 is positioned within the jacket 18 and extends from the front wall 20 toward the end wall 22 for fully dispersing the fluid flow over the entirety of the firetube 12 for maximal heat transfer. The divider wall 34 blocks any direct short circuiting of fluid flow from the jacket inlet 30 to the jacket outlet 32. The divider wall 34 extends between the firetube's first outgoing and second return legs 13, 15 and only partially toward the end wall 22 so as to accommodate the “U”-shaped bend 36 of the firetube 12 therebetween. The divider wall 34 forms a U-shaped circulation space C and flow path through the jacket 18, the heat transfer fluid P flowing from the jacket inlet 30 and all along the firetube 12 to the jacket outlet 32. In embodiments, the jacket inlet 30 can be positioned in the jacket's front wall 21 or a side wall 24 accessible outside the vessel V.

Having reference to FIG. 4, in another embodiment, the tubular jacket 18, is again external to the firetube 12 however the jacket 18 only extends outwardly toward the U-shaped bend 36 from the first and second ends 14, 16 and along a portion of both the first and second legs 13, 15 for forming the circulation space C. The first and second legs 13,15 extend through the jacket's end wall 22, while containing the circulation space C within the jacket 18. Again, a divider wall 34 can extend between the first and second legs 13, 15 only partially toward the jacket's end wall 22 for forming a U-shaped circulation space C through the jacket 18.

In yet another embodiment, shown in FIGS. 5A and 5B, the tubular jacket 18 is external to only the first leg 13 of the firetube 12 and extends outwardly therealong from the firetube's first burner end 14 towards the U-shaped bend 36. The jacket 18 can extend along a portion of the firetube 12, such as just the high temperature portion TH, or up to substantially the entire length of the first leg 13. The first leg 13 extends through the jacket's end wall 22 while containing the circulation space C within the jacket 18. The front wall 21 and end wall 22 are in the form of annular rings. One of skill would appreciate baffles, flow diverters or other forms of dividers 34 may be placed in the circulation space C to guide the heat transfer fluid P along the entirely the firetube 12 from the jacket inlet 30 to adjacent the end wall 22 and back to the jacket outlet 32.

Having reference to FIGS. 6, 7A and 7B, the tubular jacket 18 is a tubular insert, installable internal to at least the first leg 13 of the firetube 12 and extending therein from the first burner end 14 towards the U-shaped bend 36 for forming the circulation space C therebetween. The tubular insert form of jacket 18 can extend along a portion of the firetube 12, such as just the high temperature portion TH, or up to substantially the entire length of the first leg 13. In embodiments, as shown in FIGS. 7A and 7B, the internal tubular jacket 18 comprises an inner tubular wall 26 and an outer tubular wall 27, an annulus 28 being formed therebetween and defining the circulation space C. The circulation space C is enclosed by the front and end walls 20, 22. The front wall 21 and end wall 22 are in the form of annular rings. The inner tubular wall 26 defines a bore 29 formed in the jacket 18, the bore 29 being the passageway A for the flame and exhaust gases G passing through the firetube 12.

The embodiment of FIGS. 6-7B, being insertable to a conventional firetube without modification of the firetube, enables convenient and rapid retrofitting of existing process vessels V. The insert jacket 18 can be fit with a flange 20F compatible with and for securing to the burner end 14.

In one mode of operation, and having reference to FIG. 8, a jacketed firetube system 10 comprising a firetube 12, jacket 18 and circulation circuit 17, according to an embodiment, is shown fit into a heater or heater/treater process vessel 40. Any of the various jacket embodiments are equally applicable in the implementation of this system 10. The illustrated process vessel 40 comprises one or more manways 42 in a front wall 44 through which one or more of the jacketed firetube systems 10 extend. A weir 44, positioned within the process vessel 40, separates the process vessel 40 into a first containment area 46 and a second containment area 48. The first containment area 46 is adjacent the front wall 44 of the vessel 40 for receiving the contaminant-rich feedstream F, such as a polymer-rich oil/gas/water emulsion, through a feed inlet 50. The jacketed firetube system 10 protrudes into the first containment area 46 and is in contact therein with the emulsion feedstream F for heat transfer thereto. The feedstream F is exposed to heat from the firetube 12 for treatment. The second containment area 48 acts to hold the treated product fluid, such as a clean, dry product oil produced in the process vessel 40.

In an embodiment, the heat transfer fluid P is the product oil from the vessel 40. A pump 54 is fluidly connected between the vessel's second containment area 48 and the jacket inlet 30 for providing a slipstream of clean product oil as the cool heat transfer fluid P_(C) to be circulated through the circulation space C. In an embodiment, the pump 54 is a variable speed pump which is controlled by operational parameters of the system, such as the temperature of the firetube 12. As the temperature of the heated fluid P_(H) rises, the pump 54 increases the amount of the clean product oil P provided to the jacket 18 for regulating the temperature of the fluid P and the firetube 12. Maximum heat is removed from the firetube 12 and high temperatures are avoided for minimizing fouling and substantially preventing hotspots and firetube damage.

The cool product oil P_(C) is circulated within the circulation space C from the jacket inlet 30 to the jacket outlet 32, heating the product fluid P_(H) therein. As the product fluid P is compatible with the process fluid feedstream F, heat recovered from the firetube 12 by the heated product fluid P_(H) can be transferred to the process fluid F in the vessel 40 by reintroducing the heated product fluid P_(H) to the feedstream F.

In an embodiment, the jacket outlet 32 is fluidly connected to the first containment area 46, such as through the vessel's feed inlet 50. Thus, the heated product oil P_(H) is mixed with the contaminant-rich feedstream F within the first containment area 46 in the process vessel 40. Heat in the heated product oil P_(H) is transferred to the incoming contaminant-rich feedstream F, thus conserving heat in the system and reducing energy consumption required to heat the contaminant-rich feedstream F in the vessel 40.

Having reference to FIG. 9, in an embodiment a heat transfer fluid P that is not compatible with the process fluid F, such as glycol, can be circulated though the circulation space C. Heat from the heated glycol P_(H) is thereafter recovered, such as through a conventional heat exchanger 58 and the heat recovered thereby reused in the system 10, as is understood by those of skill on the art. In an embodiment, a feed stream of process fluid F is flowed through the heat exchanger 58 to recover the heat from the heated glycol P_(H). The cooled glycol P_(C) is then recirculated through the circulation space C.

Process vessels 40, such as conventional heater/treater vessels, are retrofit using embodiments of the jacketed firetube system 10.

With reference again to FIGS. 2-5, where the jacketed firetube system 10 has the jacket 18 external to the firetube, the conventional firetube is removed and the jacketed firetube system 10 inserted therein. In order to fit the externally jacketed firetube 12 within the existing manway 42, the firetube 12 within the jacket 18 is made smaller in diameter than the conventional firetube 12 removed from the vessel 40. For example, a conventional 24″ diameter firetube 12 is replaced by a 20″ diameter firetube 12 housed within a jacket 18 sized to fit the opening of the conventionally sized firetube 12 removed therefrom.

With reference again to FIGS. 6 to 7B, in the case where the jacket 18 is an insert to be fit internal to the firetube 12, the jacket 18 is dimensioned to fit within at least the first leg 13 of the firetube 12 and the jacket 18 is merely inserted therein.

As is understood by one of skill in the art, additional retrofit is required to provide a fluid connection 31 between the jacket outlet 32 and the vessel's feed inlet 50 and to provide a fluid connection 33 between the vessel 40 and the pump 54 for removing the slipstream of clean product oil P to be pumped to the jacket inlet 30, if required.

As will be appreciated by one of skill in the art, reduction in the size of the firetube 12 and removal of the slipstream of clean product oil P from the vessel 40, for circulation through the jacket 18, with subsequent reintroduction with the feedstream F, will result in only a small percentage loss of the overall capacity of the heater/treater vessel 40.

As shown in FIG. 10, in embodiments having the jacket 18 external to the firetube 12, a plurality of thermal conducting passageways 60, such as taught in Applicant's co-pending U.S. application Ser. No. 13/324,938, filed Dec. 13, 2011 and incorporated herein in its entirety, extend through the U-shaped firetube 12. Each thermal conducting passageway 60 directs cool heat transfer fluid P_(C) to be heated therethrough. Each of the passageways 60 has a thermal conductive wall 62 extending through the firetube 12 which adds to the external surface area of the firetube 12, for heat transfer to the fluid flowing therethrough.

The cool heat transfer fluid P_(C) in the jacket 18, circulated therein, is caused to pass through the thermal conducting passageways 60 enhancing heat transfer thereto. Applicant believes the cool heat transfer fluid P_(C) flows generally upwardly through the thermal conducting passageways 60 as a result of a thermosiphon effect caused by a temperature differential between the heated heat transfer fluid P_(H) above the firetube 12 and the cooler heat transfer fluid P_(C) below the firetube 12. The cool heat transfer fluid P_(C) flows from a fluid inlet 64 at a portion 66 of the circulation space C in the jacket 18 below the firetube 12 to a fluid outlet 68 at a portion 70 of the circulation space C in the jacket 18 above the firetube 12.

As one of skill will appreciate flow diverters may be positioned within the jacket 18 to enhance the thermosiphon effect urging the cooler heat transfer fluid P_(C) to flow through the thermal conductive passageways 60.

In another embodiment, as shown in FIG. 11, the thermal conducting passageways 60 are formed in the jacket 18 and the process fluid F flows therethrough as a result of the thermosiphon effect caused by a temperature differential in the process fluid F in the vessel V between heated process fluid F above the jacket 18 and cooler process fluid F below the jacket 18. 

1. A method for recovering heat from a firetube immersed in a process fluid in a process vessel, for heating the process fluid, the method comprising: circulating a cool heat transfer fluid in a circulation circuit in thermal communication with and extending along at least a portion of the firetube and therewith, for recovering heat from the firetube for heating the heat transfer fluid therein; and thereafter transferring the heat from the heated, heat transfer fluid to the process fluid.
 2. The method of claim 1 comprising: circulating the cool heat transfer fluid along at least a portion of an external surface of the firetube for recovering heat from the firetube for heating the heat transfer fluid.
 3. The method of claim 1 comprising: circulating the cool heat transfer fluid along at least a portion of an internal surface of the firetube for recovering heat from a flame therein for heating the heat transfer fluid and the at least a portion of the internal surface of the firetube.
 4. The method of claim 1 further comprising: regulating the circulation of the heat transfer fluid in response to the temperature in the firetube.
 5. The method of claim 1 wherein the heat transfer fluid compatible with the process fluid; and further comprising: mixing the heated, compatible heat exchange fluid with the process fluid in the vessel for recovering the heat therefrom.
 6. The method of claim 5 comprising: introducing the heated, compatible heat exchange fluid to a feed stream of process fluid for mixing with the process fluid in the vessel.
 7. The method of claim 5 wherein the compatible heat transfer fluid is a product fluid produced by the process vessel, the method further comprising: flowing a slipstream of the product fluid from the process vessel through the circulation circuit.
 8. The method of claim 5 wherein the compatible heat transfer fluid is a product fluid produced by the process vessel, the method further comprising: flowing a slipstream of the product fluid from the process vessel through the circulation circuit; and introducing the heated, product fluid from the circulation circuit to a feed stream of process fluid for mixing with the process fluid in the vessel.
 9. The method of claim 1 wherein the heat transfer fluid is a product fluid produced by the process vessel, the method further comprising: flowing a slipstream of the product fluid from the process vessel through the circulation circuit; and introducing the heated, product fluid from the circulation circuit to a feed stream of process fluid for mixing with the process fluid in the vessel.
 10. The method of claim 1 wherein the heat transfer fluid is incompatible with the process fluid, further comprising: flowing the heated, incompatible heat transfer fluid to a heat exchanger for recovering heat therefrom; and transferring the heat recovered by the heat exchanger to the process fluid in the vessel.
 11. The method of claim 10 further comprising: flowing a feed stream of process fluid through the heat exchanger for transferring the heat to the process fluid in the vessel.
 12. The method of claim 10 wherein the incompatible heat transfer fluid is glycol.
 13. A jacketed firetube system for transferring heat from a firetube to a process fluid in a process vessel, the firetube adapted for connection to a burner at a first burner end and a vent stack at a second outlet end and having a passageway therebetween for directing hot gases from the burner to the vent stack, the firetube being immersed in the process fluid, the system comprising: a circulation circuit extending along at least a portion of the firetube for circulating a heat transfer fluid therein, the circulation circuit comprising: a tubular jacket, extending along the firetube from the first burner end along at least a portion thereof, the jacket in thermal communication therewith and defining a circulation space therebetween; an inlet to the jacket for delivering cool, heat transfer fluid to the circulation space; and an outlet from the jacket for discharging heated, heat transfer fluid therefrom, wherein the heat transfer fluid is circulated through the circulation space for recovering at least a portion of the heat from the firetube.
 14. The jacketed firetube system of claim 13, wherein the jacket is external to the at least a portion of the firetube.
 15. The jacketed firetube system of claim 13, wherein the jacket is internal to the at least a portion of the firetube.
 16. The jacketed firetube system of claim 13 wherein the tubular jacket extends along the at least a portion of the firetube that has a surface temperature detrimental to the process fluid.
 17. The jacketed firetube system of claim 13 wherein the heat transfer fluid is compatible with the process fluid, the system further comprising: a fluid connection between the jacket outlet and the process vessel for flowing the heated, heat transfer fluid discharged from the jacket outlet for mixing with the process fluid in the vessel for recovering the heat therefrom.
 18. The jacketed firetube system of claim 17 wherein the heat transfer fluid compatible with the process fluid is the vessel's product fluid.
 19. The jacketed firetube system of claim 18 further comprising: a fluid connection between the process vessel and the jacket inlet for delivering the product fluid to the circulation space.
 20. The jacketed firetube system of claim 13 wherein the vessel further comprises a feed inlet, the system further comprising: a fluid connection between the jacket outlet and the feed inlet for delivering the heated heat transfer fluid thereto.
 21. The jacketed firetube system of claim 13 wherein the heat transfer fluid is incompatible with the process fluid, the system further comprising: a heat exchanger for flowing the heated, heat transfer fluid and a feed stream of the process fluid therethrough for transferring the heat from the heat transfer fluid to the process fluid in the vessel.
 22. The jacketed firetube system of claim 21 wherein the heat transfer fluid is glycol.
 23. The jacketed firetube system of claim 14 wherein the firetube further comprises: a plurality of thermal conducting passageways for circulating fluid therethrough, each thermal conducting passageway extending generally upwardly from a fluid inlet at a portion of the jacket below the firetube to a fluid outlet at a portion of the jacket above the firetube and having a thermal conductive wall extending through the firetube for conducting heat from the hot gases to the heat transfer fluid circulating therethrough.
 24. The jacketed firetube system of claim 14 wherein the jacket further comprises: a plurality of thermal conducting passageways for circulating fluid therethrough, each thermal conducting passageway extending generally upwardly from a fluid inlet at a portion of the vessel below the jacket to a fluid outlet at a portion of the vessel above the jacket and having a thermal conductive wall extending through the jacket for conducting heat to the process fluid.
 25. A method for retrofitting a firetube for transferring heat from a firetube to a process fluid in a process vessel, the firetube adapted for connection to a burner at a first burner end and a vent stack at a second outlet end and having a passageway therebetween for directing hot gases from the burner to the vent stack, the method comprising: inserting an insert into the first end in thermal communication with and extending along at least a portion of the firetube for forming a circulation circuit for circulating a cool heat transfer fluid therethrough for recovering at least a portion of the heat from the firetube for heating the heat transfer fluid therein. 